The main difficulty for experimental detection of the double resonances on the reservoir state frequencies is related to the fact that these frequencies are very close to the pumping frequency of the initial state. The required spectral resolution should be of the order of
the characteristic inter-level spacing, and it is not yet available. However the double resonances can be observed between two spectral well-separated intra-molecular states (see [1]}, or [2]} - [3]}). For such a case the initial (prepared by the optical pumping) and final (observed) states form a two-level system (TLS). Thus our aim in this subsection is to generalize described in the previous sections
Zwanzig model approach to study quantum dynamics of the TLS nano-systems. Note to the point that the
TLS interacting with intra-molecular and phonon reservoirs is a convenient minimal model to investigate ultra-fast molecular processes
[4]} - [5]}.
